


songs of the SOUL

by ToFightOrToFlee



Category: Undertale (Video Game)
Genre: Gen, Papyrus is great, Sans is Mysterious™, Sans is Tired™, UnderTone, again: not new, an au where i screw with battle shenanigans, but not so great at keeping secrets, but since when is that new, but that's also not new, he's also secretly a badass, pre-game, undyne is stubborn, where the music you hear when you fight comes directly from a monster's soul
Language: English
Status: Completed
Published: 2019-03-05
Updated: 2019-03-05
Packaged: 2019-11-12 04:44:59
Rating: General Audiences
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 2,735
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/18004061
Author URL: https://archiveofourown.org/users/ToFightOrToFlee/pseuds/ToFightOrToFlee
Summary: Whereas Undyne loves battle themes, Papyrus lets it slip that Sans has a particularly interesting theme, and Sans is Sans.Nobody is happy with this.





	songs of the SOUL

**Author's Note:**

> for starters, yes, UnderTone is an AU of my own making. i haven't figured out a bunch of details for it, but i had fun coming up with the ideas for this particular story! second, i play with a lot of Undertale FIGHT schematics, so tell me what you think about them if you want. third, please don't start a controversy about what songs play when you fight whoever. i'm well versed in the word of Undertale, including OSTs! if you really think i've gotten something wrong, let me know and i'll be sure to research it again. fourth, when i use past tense, i'm explaining something that's already happened. present tense is what's currently happening. and finally, enjoy the story, and let me know what you think about it!

Undyne absolutely loves battle themes. It’s the easiest way to tell a monster’s personality, she claims, because music is the sound of the SOUL. She knows the themes of almost every monster in the underground, including the less sentient ones who all seem to share the same themes. Out of them all, her favorites are her own, Asgore’s, Alphys’, and Papyrus’ (though she might be biased, once she thinks about it).

Her own theme, _Spear of Justice_ , fits her exactly. She loves the fast-paced, thrilling tune, filling her with energy and passion and, as the title implies, justice. _Bonetrousle_ is a quirky, upbeat little song that suits Papyrus almost too well. It’s bouncy and strange, just like him. Alphys’ is less of a battle theme and more her _life_ theme. It’s disjointed and awkward, mirroring her personality. Asgore’s theme is… well. Literally called _ASGORE_. Deep drums, fast beat, the sounds of string instruments melding together - the song perfectly describes the King and his legendary struggle against countless doubts and adversaries.

Yes, she loves every and all battle themes, and the monsters whose SOULs share them with her are all amazing in their own ways. She loves every monster she’s sworn to protect with her life against the despicable humans.

Except for _one_.

There’s a single monster Undyne absolutely can’t stand. His theme is awful and dorky, his personality is worse, she can’t even play-fight with him due to the fear of accidentally turning him to dust… yeah. She doesn’t like Sans even if he _is_ Papyrus’ brother. He’s her opposite in every way: tiny, weak, lazy… she could go on for hours. Papyrus insists he’s a good person deep, _deep_ down, and the only reason Undyne doesn’t completely disagree is because every monster is supposedly made up of love, hope, and compassion. Despite Sans’ (literal) shortcomings, she’s willing to give him a chance to prove himself one way or the other.

And that way is through battle.

Her plan didn’t originally start out this way. At first, she was planning on testing him by throwing situations at him and seeing how he reacted or dealt with the issue. However, it quickly became clear that he _didn’t_. React _or_ deal with the issue, that is. When Undyne asked two monsters to get into a mock fight in front of Sans’ station, the skeleton did nothing except lay his head on his arms and watch. The “fighting” monsters couldn’t keep up the charade forever and soon ended their battle, shuffling off with the sound of Sans’ applause following them. Afterward, one of them had pulled out a flier for Mettaton’s next movie, which needed more monsters to fill up the cast.

Second, she sent a Tsunderplane to ask Sans for directions. She probably should’ve picked a better monster, now that she thought about it. The plane monster hovered a dozen feet away from Sans, blushed bright pink, and said, “It’s not like I want directions to the hotel or anything.” Sans’ response was around what she expected.

“alright then, i guess i won’t tell you since you don’t want any.” And then he fell asleep. The Tsunderplane spewed a plume of smoke and retreated, embarrassed. More so than usual.

So no, testing wasn’t working. At all. During a training session with Papyrus, she had been fully prepared to take him aside at the end and tell him that unfortunately, she’d have to let his brother go. He only did the bare minimum of work to keep his position(s?), nothing more or less. It was almost impressive, but Undyne knew there were plenty more monsters out there who would go above and beyond. _Those_ were the monsters the Royal Guard needed.

So she grabbed Papyrus’ shoulder before he could run home, opened her mouth, and said, “We need to talk about your brother.”

“OH! ALRIGHT!” Papyrus agreed, no hesitation at all. Undyne almost felt bad, knowing she was about to smash that trust into little bits. “WHAT ABOUT?”

“His performance,” Undyne said, tone grave, and Papyrus wilted. “Sorry, Paps, but he’s just… too…”

“LAZY?” Papyrus finished for her. She nodded. “WELL… YES, IT’S TRUE THAT MY BROTHER IS VERY LAZY _NOW_ , BUT YOU SHOULD’VE SEEN HIM WHEN WE WERE STILL BABY BONES! IF HE FOUND A SOURCE OF MOTIVATION, I’M SURE HE’D BE GREAT ONCE AGAIN! HE TAUGHT ME HOW TO USE BLUE MAGIC SO PRECISELY! I REMEMBER ASKING HIM ONCE WHY HE NEVER FOUGHT ME HIMSELF AND INSISTED PRACTICING ON TREES… WOWIE! THAT WAS THE ONLY TIME I HEARD HIS BATTLE THEME, BUT I HAVEN’T FORGOTTEN IT! I NEVER KNEW MY BROTHER WAS SO COOL!” Papyrus’ empty eye sockets were somehow sparkling. Undyne gaped at him like… well, like a fish.

“But… his theme’s so dorky! And weird!” she spluttered. “Didn’t you hear it when he took the initiation test?!” Papyrus shook his head.

“HE HAS TWO THEMES! I DON’T KNOW WHY, BUT I NEVER ASKED BECAUSE I KNOW HE WON’T ANSWER! THE ONE YOU’RE THINKING OF IS HIS NORMAL THEME, _SANS_ , AND I AGREE. IT’S VERY SILLY! THE NAME AND THE SONG! BUT HIS BATTLE THEME… I BELIEVE IT WAS CALLED…” He paused, recalling. Undyne felt her fins bristle, the weight of some unseen power settling over her. The world seemed to darken until it was only her and Papyrus. “ _MEGALOVANIA_.”

The weight disappeared. Papyrus beamed.

“I ENJOYED SPEAKING WITH YOU, UNDYNE! BUT NOW I MUST RETURN HOME SO I CAN MAKE DINNER! I’LL KEEP YOUR ADVICE ABOUT POUNDING THE TOMATOES IN MIND!” He saluted, turned, and fled. Undyne’s goal changed from firing Sans to finding a way to make him fight her for real. If he was really as talented with magic as Papyrus said, if the music of his SOUL was so intense and life-changing enough that she could _feel_ the weight of only the name…

She had to hear it for herself.

Which is why she’s standing in front of her house right now, impatiently fidgeting and waiting for Papyrus to show up with his brother while Mad Dummy watches her judgingly. He knows better than to actually say anything - Undyne won’t hesitate to beat the stuffing out of him. Again. She doesn’t tend to hold back when her opponent can’t feel pain and has the ability to pull himself back together. Of course, she has to  _pay_ him every time he stitches himself up, but it’s a small price for the satisfaction of releasing her “passion” through unrestrained violence and screaming.

She always hears Papyrus before she sees him. In these caves, things echo, and not just because of the magic flowers. His words carry ridiculously far, so when she hears the first faint echoes of Papyrus’ naturally loud voice, she knows he’s still a few minutes off but closing in. She can’t hear his brother, but that’s normal. Whereas Papyrus is loud and attention-grabbing, Sans is quiet and easily overlooked.

She starts bouncing in place as Papyrus’ voice grows closer and closer, fingers flexing on the shaft of her spear. It’s a magical one, green and crackling with energy, and she knows if anyone besides her tries to touch it, they’ll get a nasty shock. It’s one of her favorite things about her magic: it’s volatile and dangerous, just like her. She grins, twirls the spear around a couple times, and then lets it vanish just as a red boot pokes around the corner.

“I’M JUST SAYING,” Papyrus says, very loudly as he steps in and catches Undyne’s eye, “THAT THIS COULD BE GOOD FOR YOU, BROTHER! I HAVEN’T SEEN YOU PRACTICE YOUR MAGIC OR TRAIN SINCE… EVER! IT’S UNHEALTHY! WHAT IF AN EVIL HUMAN COMES? WINK!” He gives a very unsubtle wink and steps aside. Behind him is a much smaller figure, somehow looking simultaneously exhausted and wide awake. Like he’s chugged four cups of coffee after a sleepless night.

“i’ll be fine,” Sans says, then breaks off to yawn. Undyne stares a moment too long into the inky, empty blackness of his mouth, morbidly fascinated. There’s a tiny gap between his front teeth. “the human’s gotta catch me, first.”

“That wouldn’t be hard,” Undyne growls, crossing her arms and glaring down at the skeleton. He neutrally blinks back, teeth clicking shut. “You’re always sleeping or sitting still! All a human would need to do is walk up at the wrong time and _bam_!” She claps her webbed hands together, making Papyrus jump theatrically and Sans stare. “You’d leave Papyrus all alone! Is that what you want?!” The taller skeleton gasps with an appropriate amount of horror, clasping his hands to his face. Sans gives off the impression of raising an eyebrow despite having no eyebrows to speak of.

“no, not really,” he says slowly. “is there a point to this? i don’t think you wanted me to come here so you could lecture me about work ethics.” Apparently, he can read the situation better than Undyne thought. He _knows_ something’s up, that Papyrus’ invitation for him to join the training session was planned and not spontaneous. Her limited patience snaps.

“To hell with the script!” she screeches in Papyrus’ general direction, then points an aggressive finger at Sans. “Fight me!”

“UNDYNE!” Papyrus wails, stamping his feet. “YOU SKIPPED TEN MINUTES’ WORTH OF DIALOGUE! WE WERE SUPPOSED TO EASE HIM INTO THE IDEA! NOW HE’LL JUST SAY NO AND LEAVE!”

“okay,” says Sans.

“SEE? HE... AGREED?” Papyrus twirls around, eyes googly. “SANS! YOU AGREED?”

“sure.”

“WOWIE! I THOUGHT WE’D HAVE TO WAIT HALF A YEAR TO CATCH YOU OFF GUARD AND ASK YOU TO COME, THEN FORCE YOU TO AGREE. I’M GLAD TO SEE THIS ISN’T THE CASE!” Papyrus beams, clasps his gloved hands together, and steps back. “I HAVE ONLY GOOD FEELINGS ABOUT THIS! ...MOSTLY GOOD. UNDYNE, PLEASE DON’T KILL MY BROTHER.”

“You _bet_ I will!”

“I SAID _DON’T_ -!”

Undyne reaches out with her magic, grinning wildly. Sans responds in kind. Cool, lazy blue magic connects with the fiery, fierce blaze of Undyne’s power. There’s three timely clicks, the world around them falls away, and it’s just Sans and Undyne. Papyrus hovers just outside the range of the FIGHT, twisting his gloved hands together. He looks eager. There’s a brief moment of silence.

 _Spear of Justice_ starts with a bang, making Papyrus and Undyne flinch.

“No, _no,_ **_no_**!” Undyne snarls, slamming down on SPARE. Sans tilts his head and accepts it, the wet caves of Waterfall fading back in and the sound of aggressive percussion dying out. Undyne breathes heavily. Papyrus makes a disappointed little sound and hangs his head.

“something wrong?” Sans asks. “that wasn’t exactly the thrilling battle i had in mind.” He rocks back on his heels.

“ _Y_ _ou’re_ supposed to take charge of the music!” Undyne hisses, levelling the smaller skeleton with a one-eyed glare. “I listen to my own theme all the time! Now it’s _your_ turn, idiot! Let me hear your SOUL!” This time, she crosses her arms and waits for Sans to instigate the FIGHT. He stares for a long, tense moment before Undyne feels the prod of his magic. Teeth bared, she reciprocates.

_Click._

_Click._

_Click._

Color leeches away. Undyne sets her jaw and taps her claws against the scales of her upper arms. Sans’ grin is impassive. Waiting.

 _sans_ blares, and her fins press against her head with agony.

“ _No_!” she bellows, slamming her fist into the inactivated FIGHT. Sans closes his right eye, looking annoyed, and  - _ping_ \- offers MERCY. Undyne accepts the SPARE, the FIGHT ends, and the music stops. She allows her fins to flare back out with anger.

“what’s wrong this time?” Sans sighs. “you asked. i provided. what more do you want?”

“I wanna hear your theme,” Undyne says, voice low and dark, and she sees the confusion in his eyes. “None of those goofy _noises_ you call your song. I want _your_ theme. The one Papyrus called _Megalovania_.” Once again, even uttering the name makes her feel as if her sins are crawling on her back. The bright little lights in Sans’ eye sockets blink out. He looks eerie.

“oh,” he says quietly. “is that so?”

“SORRY, SANS,” Papyrus mutters, looking at the ground. “SHE WAS GOING TO FIRE YOU! I THOUGHT IF SHE KNEW HOW GREAT YOU ARE - HOW GREAT THE MUSIC OF YOUR SOUL IS - SHE WOULD RETHINK!”

“Wait, you knew I was-?”

“it’s cool,” Sans says, reaching to pat Papyrus’ elbow. “don’t worry about it, bro. it was gonna happen eventually, right? might as well get it over with now. i guess in this case, procrastination really isn’t an option.” He shrugs, hands level with his shoulders, and some light fades back into his eyes. “ready when you are, fish face. and this time, no holding back.” His smile grows wide. Undyne cheers.

“Hell yeah! That’s more like it!” Their magic clashes. She impatiently taps her foot in time with the clicks, teeth showing in a feral smirk. This time around, there’s a strange pressure when the FIGHT initiates, heavy and fully expected. She shuffles her feet to continue standing tall, gaze locked with the small skeleton before her. One beat. Two. Three.

 _Megalovania_ , her head murmurs, and the song begins.

It’s a simple beginning. A single sound, fast-paced, notes bouncing up and down. She can feel this isn’t it and waits, claws hovering over FIGHT. It isn’t her turn, not yet, but Sans doesn’t seem keen on truly beginning the battle. He stands calm and still, hands not in his pockets like she thought they would be, but linked together behind his back. The bass hits. Deep, thrumming, definitely not all he has to offer. She flexes her fingers and grinds her teeth. Standing is just a bit more difficult than it was a moment ago. Papyrus looks concerned.

The faint sound of a cymbal is all the warning she gets before she’s bowled over by sound, power, the sheer presence of _noise_ , overwhelming her every sense until all she knows is _Megalovania_. Her scales bristle to make her look larger, fins flatten, her remaining eye squeezes shut. She doesn’t fall, but it’s a near thing. Her hands rise up and clamp down on her temples, a shriek escaping her mouth before she can stop it. There’s a _ping_. When she musters up the strength to look, Sans’ name before her is yellow.

Sans is sparing her.

She accepts. The assault on her consciousness disappears. Papyrus runs forward to steady her before she collapses with relief, eye sockets wide.

“UNDYNE!” he yells, and though his voice is loud, it’s nowhere near the volume of _Megalovania_. She never thought she would associate _Papyrus_ with the word _quiet_. “UNDYNE, ARE YOU ALRIGHT? I’M SORRY, I SHOULD’VE WARNED YOU ABOUT THAT! _SANS_ SHOULD’VE WARNED YOU ABOUT THAT! I UNDERSTAND IT CAN BE QUITE OVERWHELMING WHEN YOU EXPERIENCE IT FOR THE FIRST TIME, BUT OVER THE YEARS, I THOUGHT IT WOULD GET BETTER-!”

“I’m good,” Undyne croaks, patting Papyrus’ skull and cutting him off. “I’m fine. Lemme go.” He makes sure she can stand, lets go, and backs off. He knows she isn’t about to take his brother down in this state. She wobbles forward, crouches down a foot away from Sans, and just looks. He slowly blinks.

“you missed the best part,” he says. “should’ve lasted about ten seconds more. too bad.”

“Why the hell,” Undyne wheezes, “is your theme so _badass_?!” The corners of Sans’ lopsided grin twitch. He reaches out, rests a delicate hand her shoulder, and shakes his head.

“oh, undies,” he sighs. “didn’t the dogs tell you? i can handle myself in a fight if i have to. _secretly_ badass. don’t tell anyone, okay? it’ll ruin my reputation. shh.” He brings a finger to his teeth. Then he turns and takes a few steps toward Mad Dummy, intent on sparking conversation.

Suddenly, he stops. His head tilts slightly and he peers over his shoulder. His mouth curls upward.

“oh, and i probably should’ve said so in the beginning, but… _megalovania_ isn't mine. i just like borrowing it sometimes because it sounds cool.” He continues walking, whistling _sans_ through the gap in his front teeth.

Undyne howls with frustration. Papyrus’ hand smacks into his face with a groan. Mad Dummy revels in the madness.

Unseen, a child wakes up in a patch of golden flowers, music pounding within their SOUL.


End file.
